How to Configure DHCP Option 150 on Cisco Routers and Switches

DHCP Option 150 is critical in Cisco Unified Communications deployments, allowing IP phones to automatically discover their TFTP server for configuration and firmware downloads. Proper configuration ensures phones register successfully and can be zero-touch provisioned.

For understanding what DHCP Option 150 is, refer to: What Is DHCP Option 150 and How Does It Work?

Basic Configuration Principles

DHCP Option 150 is configured only on DHCP servers, not on TFTP servers or every network switch.

Supported DHCP servers include:

• Cisco routers (IOS and RV series)
• Certain Cisco switches (e.g., SG350) acting as DHCP servers
• Microsoft Windows DHCP server
• Third-party DHCP servers such as FortiGate

Cisco Router CLI Configuration Example

configure terminal
ip dhcp pool VOICE_PHONES
 network 192.168.10.0 255.255.255.0
 default-router 192.168.10.1
 dns-server 8.8.8.8 8.8.4.4
 option 150 ip 192.168.10.10
exit
end

Replace 192.168.10.10 with your actual TFTP server IP.

Cisco Switch CLI Configuration Example (e.g., SG350)

configure terminal
ip dhcp server enable
ip dhcp pool VOICE_POOL
 network 192.168.2.0 255.255.255.0
 option 150 ip 192.168.2.10
 default-router 192.168.2.1
 dns-server 8.8.8.8
exit
end

Multi-VLAN Considerations

For environments with multiple VLANs, configure Option 150 separately on each VLAN's DHCP scope so phones in each VLAN can access the correct TFTP server.

Zero-Touch Deployment Preparation

• Ensure the TFTP server has correct configuration and firmware files, especially xmldefault.cnf.xml.
• Clear phones’ trust lists when performing firmware migrations.
• Test deployments in a controlled environment before large-scale rollout.

Troubleshooting Tips

• Verify Option 150 IP is correct and DHCP scopes are active.
• Confirm network connectivity between phones and TFTP server.
• Ensure TFTP service is running and files are accessible.
• Check phone logs for errors.
• Understand differences between Option 150 and 66 to avoid misconfiguration. For details, see DHCP Option 150 vs Option 66: Key Differences.

FAQ

Q1.How do I configure Option 150 on a Cisco router?

Enter DHCP pool configuration mode and use option 150 ip .

Q2.Do Cisco switches support Option 150?

Some do, such as the Cisco SG350.

Q3.What are common issues with Option 150?

Incorrect TFTP IP, network connectivity issues, or missing files on TFTP server.